I know that the Logitech Speakers like my Z5300's and my brother's X230's come with adapters so you can hook stuff like XBox, PS2, TV's, and stuff like that right to the speakers. By the way these Z5300's are THX certified which doesn't mean much. If you want the amazing DTS then your going to need a decoder. The X-Fi cards do come with DTS encoding built in. The Logitech Z5500's also come with DTS hardware decoding but it is not neeccessary if you alreadly hav e the encoding capabiliteis with the sound card.
If you are looking for DTS with your XBox 360 or whatever your hooking up to it you may need to get someting with Built In DTS hardware encoding. (I believe the XBox 360 does but someone should verify that.)